1. Field of the Invention
The present invention relates to surface acoustic wave filters capable in particular of using one-directional DART type transducers.
2. Discussion of the Background
This type of transducer has the advantage of sending or receiving an acoustic wave essentially in one direction. This greatly improves the efficiency of the transducer. It is formed by a set of transducer centers and reflection centers whose distribution makes it possible to obtain very valuable filtering characteristics. However, owing to their design, DART filters are devices whose length is relatively great, typically several hundreds of .lambda., if .lambda. is the wavelength at the central frequency of operation of the device.
Consequently, a filter comprising two DART type transducers, one at input and the other at output, requires the use of a substrate whose length is appreciably greater than its width. It then becomes necessary to use a non-standard package, itself having a length appreciably greater than its width, which is difficult to incorporate into the usual systems of implantation, and which furthermore has weaknesses in torsion and deflection.